Showing papers on "Mass transfer coefficient published in 1969"

Effects of transpiration and changing diameter on heat and mass transfer to spheres

Abstract: Mass transfer to spheres suspended in an agitated liquid has been studied both experimentally and theoretically. Finite-difference solutions are obtained for mass transfer from a sphere to a fluid flowing past it in steady viscous flow. The effects of a transpiration velocity at the surface of the sphere and of a continuously changing sphere diameter are included. A normalized presentation of these effects is quite insensitive to the bulk flow Peclet number. When these theoretical corrections for transpiring and shrinking spheres are applied to the mass transfer data for ice spheres that are melting in an agitated brine bath, the corrected mass transfer coefficients are brought into agreement with a generalized correlation published elsewhere. This agreement suggests that the theoretical results apply, with reasonable accuracy, to a shrinking and transpiring sphere that is suspended in a turbulent liquid.

Effects of surfactants on mass transfer inside drops

Abstract: A model is presented to account for reduced mass transfer to drops falling through a continuous phase which contains a surface active agent. The fluid flow patterns are essentially laminar. The reduction in mass transfer is said to be due to a reduction in available interfacial transfer area and to changes in both velocity and pattern of internal circulation. These are shown to be functions of contact time and can be characterized. Experimental values agreed with the theoretically predicted ones with a deviation of less than 10%.

Use of electrochemical techniques to study mass transfer rates and local skin friction to a sphere in a dumped bed

Abstract: Electrochemical techniques are developed to study the details of the flow around a single particle in a packed bed. Initial work has been done with a dumped bed of 1 in. spheres. Results are presented on the variation of the mass transfer coefficient and the shear stress around the surface of one of the spheres, the overall mass transfer rates to a sphere in a bed of inert spheres, and the effect of Reynolds number on the local mass transfer coefficient and the shear stress.

Mass and heat transfer relations in evaporation through porous membranes

Abstract: This study concerns rates of evaporation and mass transfer of water vapor from a heated salt solution through a water repellent porous membrane to a cooled water condensate. This transfer is a result of temperature differences and corresponding vapor pressure differences across the membrane. Three groups of experiments were carried out which indicate that the major factor influencing the rates of transfer is diffusion through a stagnant gas in the membrane pores. However, an equation considering film heat transfer coefficients, membrane thermal conductivity, and an empiricial correction based on temperature driving force appears to be necessary for representing all the data. The empirical correction appears to be related to internal condensation and possibly diffusion along surfaces.

Transport phenomena at the wall of agitated vessels

Abstract: This paper deals with an experimental study on the local factors of friction in tangential direction and mass transfer coefficients on the wall of an agitated vessel with paddle type impellers as agitators, and with a discussion of the analogy between momentum and mass transfer phenomena. Experimental results show that the average factor of friction and j factor of mass transfer are correlated the same equation with respect to Reynolds number, and that the vertical distributions of local factors of friction in tangential direction and those of mass transfer coefficients are quite similar. Besides this it is found that the peak of the distribution curve at the height of the impeller is caused by jet flow issuing from the impeller, while the flat part of the curve is attributed to rotating flow. Finally the measured values of the local mass transfer fluctuation intensity were plotted in a diagram.

Transfer of Oxygen in Aqueous Solutions

Abstract: The paper reports the results of studies which describe the influence of geometry and temperature on the liquid film coefficient, \IK\N\DL\N, and the mass transfer coefficient, \IK\N\DL\Na, for the transfer of oxygen from air bubbles rising in a liquid. It is shown that the liquid film coefficient is related to the total drag force operating at the liquid gas interface. The influence of several surface active agents on KLa and KL are reported. The study indicates that at low concentrations, the principle influence of surface active agents is their effect on the bubble size and rate of rise.

Growth models of cultures with two liquid phases. III. Continuous cultures

Abstract: Some mathematical models, which have been used to describe batch growth in fermentations with two liquid phases present, are used to predict the behavior of continuous fermentations in a chemostat. Two types of dispersed systems are considered in this investigation. In the first, type, it is assumed that the composition of the dispersed phase is such that, increased substrate utilization results in a decreased substrate concentration with no change in the interfacial area. In the second type of system, the dispersed phase is assumed to be pure substrate; therefore, the substrate concentration in the dispersed phase remains constant but the interfacial area is affected by changes in dilution rate. Three special cases are examined for each type of system in order to examine the effect of the interfacial area, the phase equilibrium constant, and the mass transfer coefficient on system performance. Comparison of two of the models with available experimental data shows fair agreement, between model and data.

Simultaneous gas‐liquid interfacial mass transfer and uptake by small particles

Abstract: The presence of active small particles, such as bacterial cells, in a liquid will affect the rate of gas-liquid interfacial mass transfer. A theoretical analysis of the situation is presented in this article.

Specification, Selectivity, and Performance of Porous Cellulose Acetate Membranes in Reverse Osmossis

Abstract: : The general specifications of the Loeb-Sourirajan type porous cellulose acetate membranes are given in terms of the pure water permeability constant, A, and the solute transport parameter for sodium chloride at different operating pressures. A scale of membrane selectivity is presented for 12 inorganic and two organic solutes in terms of their relative values of the solute transport parameter for several membrane specification and selectivity, and the applicable mass transfer coefficient, k, obtained from a generalized correlation, the performance data for different membranes solution systems, and operating conditions have been calculated. These data related membrane specification to membrane performance expressed in simple terms of solute separation and product rate. The effects of variation of the solute transport parameter, feed concentration, feed flow rate, operating temperature, A-factor (membrane compaction), and chemical nature of solute on membrane performance are illustrated and discussed. The order of solute separation with respect to any two solutes does not always correspond to that of their relative values of the solute transport parameter, and the former is a function of the latter and the operating conditions of pressure, feed concentration, and the mass transfer coefficient, k. (Author)

Some general equations for reverse osmosis process design

Abstract: : A generalized approach to reverse osmosis process design is presented for solution-membrane-operating systems characterized by the dimensionless parameters gamma, delta, and lamba defined in terms of the pure water permeability constant A, solute transport parameter, mass transfer coefficient k on the high pressure side of the membrane, and the properties of the solution. Analytical expressions are derived, in terms of dimensionless quantities, for the change of volume of solution, concentration of the bulk solution and that of the concentrated boundary solution on the high pressure side of the membrane, the change in the permeating velocity of solvent water through the membrane, solute separation, and the other related quantities, at any instance, as a function of concentration of the product solution on the atmospheric pressure side of the membrane, or time from the start of the operation for reverse osmosis systems specified by gamma, delta, and lamda. The equations are developed first for the case of batch-by-batch operation, and their applicability to the flow case is then indicated. (Author)

Mass Transfer of Rough Hailstone Models in Flows of Various Turbulence Levels

Abstract: The convective mass transfer of smooth and rough sphere test particles over a range of Reynolds numbers between 3 × 103and 105 was studied by means of an electrochemical method at a Schmidt number of 2170. The experiments were carried out in a liquid tunnel where the electrolyte is forced past the stationary test particles at variable flow rates. Three distinctly different levels of turbulence intensity of the flow allowed an evaluation of the turbulence effect on the transfer rates. An extrapolation of the results to the heat and mass transfer coefficients of hailstone models in the atmosphere shows that surface roughness may account for increases in the transfer rates of up to a factor of 2. For relatively large roughness elements (cluster Particles) the increase in the convective transfer coefficients at equal Reynolds numbers (based on equal volume diameters) is approximated by the increase in surface area. Atmospheric turbulence is not expected to change these transfer coefficients significa...

Mutually dependent heat and mass transfer in laminar duct flow

Abstract: An analysis is performed of the strongly coupled heat and mass transfer processes which result from sublimation of mass from the walls of a duct into a flowing gas, the latent heat being provided solely by convective transfer from the gas. The flow is assumed to be laminar and hydrodynamically developed. Results are given for the streamward variations of the bulk and wall temperatures and mass fractions, of the heat and mass transfer rates, and of the local heat transfer coefficient. Representative temperature and mass fraction profiles are also presented. Entrance lengths characterizing the near approach to fully developed conditions are tabulated. Comparisons are made of the present results (based on a parabolic velocity profile) with those based on a slug flow velocity profile. A subsidiary analysis using the Levěque model is also performed and the results compared with those of the principal solution.

Generation of an Evaporation Time Series for Lake Ontario

Abstract: Monthly mean values of evaporation from Lake Ontario for the period from 1872 to 1965 inclusive were generated by a mass transfer procedure. Available onshore recorded meteorologic data were adjusted to obtain approximate over lake values with empirically derived equations. The mass transfer coefficient was calculated by using an equation proposed by Harbeck [1962] relating the coefficient with water surface area. A comparison of the generated mass transfer evaporation data with water budget estimates obtained by Morton [1967] revealed that on the average the two methods gave similar results.

Effect of liquid‐packing surface interaction on gas absorption and flooding in a packed column

Abstract: Gas absorption, pressure drop, liquid holdup, and loading behavior in a packed column have been investigated using packing materials almost geometrically identical but fabricated from three different materials (ceramics, Saran, and polyethylene). For the absorption of oxygen into sodium sulfite solution, observed values of the liquid-side, composite, overall mass transfer coefficient, KLa, were about 25% larger for the ceramic packing than for the polymeric packings. It was also observed that liquid loading occurs more readily in the case of the polymeric packing materials and it appears that the usual type of correlation is inadequate for predicting loading when polymeric packings are employed. In the case of liquid operating holdup no differences were observed from packing to packing. These observations are discussed in terms of the nature of the interaction between liquid and packing surface and it is pointed out how these phenomena may be fundamentally different from those of previous investigations, which relied upon surface-active agents added to the liquid.

Influence of Molecular Properties of the Fluid on Simulation of the Total Heat and Mass Transfer of Solid Precipitation Particles.

Abstract: Heat transfer measurements from a smooth and a rough (lobe structured) sphere to water (Prandtl number Pr = 7) at Reynolds numbers 3 × 103 < Re < 7.5 × 104 are described and compared to mass transfer measurements made previously under identical flow conditions but at Schmidt number Sc = 2170. The comparison shows how the molecular properties of the fluid affect the transfer of smooth and rough particles and, by inference, how the results of transfer measurements in liquids can be applied to air. The new measurements help to establish a safer basis for model experiments. They essentially confirm previously made extrapolations on the roughness effect on the convective heat and mass transfer of spherical hailstones.

Unsteady-state models of gas absorption columns

Abstract: The unsteady-state equations for a plate gas absorption column are formulated. The equations take into account imperfect plate efficiencies and liquid flow changes. Transfer-function and state-variable models of the column are derived. Experimental frequency responses are obtained on a 4-in. i.d., six-plate laboratory absorption column operating with the system air–ammonia–water and are compared with the theoretical responses. The unsteady-state equations for a packed gas absorption column are also formulated, taking into account variations of mass transfer coefficient and interfacial area and liquid flow changes. A transfer-function model of the column is derived. [Continues.]